1. Field of the Invention
The present invention relates to a mask for fabricating a large sized display panel.
2. Background of the Related Art
Recently, a size of the display panel becomes the larger as high quality, and high resolution of a picture are pursued. However, there are many technical difficulties in fabrication of such a large sized display panel, of which is a difficulty of fabrication process caused by the mask used in fabrication of the large display panel, i.e., a size of the mask is required to be large for fabrication of the large sized display panel.
However, the fabrication of such a large sized mask, not only requires much time and cost, but also has a disadvantage of poor accuracy in fabrication process caused by sagging of the mask. For an example, for fabrication of an organic EL display panel, a shadow mask of a strip type as shown in FIG. 1A, or a delta type as shown in FIG. 1B, is required for deposition of luminescent material layers of R, G, B pixels invariably. However, those masks are liable to sag due to patterns on the masks, to damage barriers and the like formed on the panel during deposition of the material, particularly, the strip type shadow mask in which rectangular elongated patterns are formed has a greater sag than the delta type shadow mask.
Referring to FIG. 2, the sagging of the shadow mask becomes more greater when unit devices are mass produced on a large sized substrate, because, as shown in FIG. 3, the size of the shadow mask is required to be large the same as the substrate, and many patterns are formed on the shadow mask.
To cope with this problem, a tension is applied to the shadow mask, which however causes deformation of the mask patterns, i.e., distortion, or elongation, that makes accuracy of the deposition process poor, to limit a size of the mask.
Moreover, even if a shadow mask with no sagging is used, metal stripes on the mask are susceptible to vibration even by a weak impact, to give damage to the barriers of the panel. That is, since a gap between the shadow mask and the panel is very small, the vibration to the mask gives damage to the barriers at the highest positions among the barriers formed on the panel, which may cause shorts between pixels in fabrication of second electrodes.
However, one attempt to provide a larger gap between the shadow mask and the panel for preventing the damage to the barrier results in deposition of the materials at inaccurate positions due to a shadow effect that causes another problem.